Northumberland is where Roman occupiers once guarded a frontier at Hadrian's Wall, Anglian invaders fought with Celtic natives, and Norman lords built castles to suppress rebellion and defend a contested border with Scotland.

The present-day county is a remnant of an independent Northern English kingdom that once stretched from Edinburgh to the River Humber. Reflecting its tumultuous past, Northumberland has more castles than any other county,[1] and the greatest number of recognized battle sites. Once an economically important region that supplied much of the coal that powered the industrial revolution, Northumberland is now a rural county with a small and gradually shrinking population.[2]

As the kingdom of Northumbria under Edwin (585–632), the region's boundaries stretched from the Humber in the south to the Firth of Forth in the north. The kingdom and county were named for the Humber.